Binary burner with Venturi tube fuel atomization and Venturi jets for the atomization of liquid fuel

ABSTRACT

A burner, in particular, for a motor vehicle supplementary or parking heater, for the burning of liquid fuel, in the presence of combustion air, has a combustion chamber ( 10 ), with a jet for the atomization of liquid fuel, arranged before said chamber. The jet has a Venturi tube ( 11 ) at the largest diameter end of the diffuser section thereof, opening into the combustion chamber ( 10 ), and the liquid fuel is introduced into the Venturi region which is at a low pressure when compared with the upstream end of the diffuser section ( 12 ), and through the inlet section ( 13 ) of which the air is pumped.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a binary burner for an auxiliary motor vehicleheater, for combustion of liquid fuel in the presence of combustion air,with a combustion chamber which is downstream of a nozzle foratomization of liquid fuel, and a Venturi nozzle for atomization ofliquid fuel.

2. Description of Related Art

German Patent DE 41 18 538 C2 discloses an example of a burner of theinitially mentioned type. This burner is based on a dual-fuel nozzle foratomization of fuel which has a relatively complicated structure. Inparticular, this nozzle consists of an essentially cylindrical mixingchamber, a feed pipe coaxial to its lengthwise axis for the liquid fuel,and a combustion air medium feed. The mixing chamber of the nozzle isclosed by a nozzle insert for discharge of the atomized fuel/combustionair mixture and has a central nozzle hole and a conical inner bevelwhich converges in the flow direction. The combustion air feed consistsof a feed pipe which tangentially penetrates the mixing chamber wall,dips into it and discharges at a greater height above the nozzle insertthan the feed pipe for the liquid fuel. Due to this complex structure ofthe dual-fuel nozzle, for its proper operation for atomization of theliquid fuel, a considerable air overpressure is required which must beapplied by a correspondingly powerful fan.

In conjunction with the gas burners, use of Venturi tubes as a mixingmeans is known. Furthermore, U.S. Pat. No. 4,396,372 discloses a burnersystem in which liquid fuel in the form of kerosene is delivered bymeans of a nozzle to a vaporizer provided with electrical heating means,with a Venturi-shaped inlet area.

SUMMARY OF THE INVENTION

One object of this invention is to devise a burner or a Venturi nozzlefor atomization of the liquid fuel which does not require a high airoverpressure for atomization of the liquid fuel and which operatesreliably.

This object is achieved by a burner with nozzle having a Venturi tube ora Venturi nozzle with an inlet part which tapers in the flow directionof the combustion air and with a diffuser part which widens in the flowdirection of the combustion air, the larger diameter end of the diffuserpart discharging the liquid fuel into the combustion chamber, in theunderpressure area in the transition area from the inlet part to thediffuser part, and by a Venturi nozzle that is axially divided into afuel/combustion air discharge part and a fuel/combustion air supplypart, the two Venturi nozzle parts being heat insulated relative to oneanother.

Accordingly, in accordance with the invention, the complex nozzle usedfor the binary burner is replaced by an arrangement with a Venturi tubeor a Venturi nozzle, which to prevent coking and heat losses is made atleast partially of a ceramic material. As a result of the pressurerecovery of the Venturi tube or the Venturi nozzle it is not necessaryto deliver air with a high overpressure so that the strong fan oradditional fan which had been necessary in the past for this purpose canbe omitted. The Venturi tube (or Venturi nozzle) used in accordance withthe invention, moreover, has the advantage that economical production ispossible.

Both the installation cost as well as the production costs areadvantageously reduced if at least the front section of the Venturidiffuser part or the Venturi nozzle is made integral with the combustionchamber.

In the simplest case, the diffuser part of the Venturi tube or Venturinozzle is formed with a uniform opening angle. However, according to oneadvantageous development, this Venturi tube or Venturi nozzle diffuserpart can have sections of different opening angles, the section with thegreatest opening angle bordering the combustion chamber.

Advantageously, the fuel is supplied to the Venturi tube or Venturinozzle via a fuel feed tube with downstream end projecting into theVenturi tube. This downstream end of the fuel feed tube can dischargeinto a downstream dual-fuel nozzle or into the underpressure area of asecond smaller Venturi tube which is operated in turn by the pressuredrop of the Venturi tube or Venturi nozzle and ends in its underpressureregion in order to achieve pre-atomization. Furthermore, the fuel feedtube is advantageously located within the Venturi tube or Venturi nozzlerunning coaxially to its lengthwise center. The downstream end can belocated at different locations of the Venturi tube or Venturi nozzle,for example, in the inlet part or in the diffuser part of the Venturitube or the Venturi nozzle or at its narrowest site between the inletpart and diffuser part.

Furthermore, it is advantageously provided that the combustion chamberhave at least one additional inlet for secondary air. This secondarycombustion air inlet is preferably located in the plane of thecombustion chamber in which the Venturi tube or Venturi nozzledischarges.

The invention is explained below by way of example using the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows half of a lengthwise section of thecombustion chamber and Venturi tube according to one embodiment of thedual-fuel burner,

FIG. 2 shows a diagram of the axial pressure variation in the Venturitube shown in FIG. 1,

FIG. 3 shows one variant to FIG. 1 with a small Venturi tube instead ofa nozzle for fuel atomization, and

FIG. 4 shows a Venturi tube with an axial separation site in the area ofthe diffuser.

DETAILED DESCRIPTION OF THE INVENTION

The dual-fuel burner in accordance with the invention comprises acombustion chamber 10 of a preferably cylindrical or cuboidal shape. AVenturi tube 11 is connected to the fuel/combustion air inlet side ofthe combustion chamber 10. The Venturi tube 11 which forms the Venturinozzle is formed preferably, at least in the connection area, integrallywith the combustion chamber 10.

The Venturi tube 11, in the conventional manner, has a diffuser part 12and an inlet part 13. The diffuser part 12 has a longer axial extensionthan the inlet part 13 and preferably has a conical shape, the end withthe largest diameter of the conical diffuser part 12 being connected tothe fuel/combustion air inlet of the combustion chamber 10. The inletpart 13 which, likewise, has a conical shape or at least one inlet radiiwith an optionally connected cylindrical part, with a section ofgreatest diameter pointing away from the combustion chamber 10, adjoinsthe end of the diffuser part 12 which is smallest in diameter.

The Venturi tube 11 and the combustion chamber 10 are preferably on acommon lengthwise central axis 14. The fuel feed tube 15, with adual-fuel nozzle 16 being connected to its downstream end, is flush withthis lengthwise central axis. The outlet opening of the dual-fuel nozzle16 lies at the narrowest point between the diffuser part 12 and theinlet part 13 of the Venturi tube 11, i.e., in an area at a lowerpressure relative to the combustion chamber 10, as illustrated in FIG.2.

Instead of the dual-fuel nozzle 16, according to the version shown inFIG. 3, there can also be a small Venturi tube 19 at the same locationwhich is operated by the pressure drop of the Venturi tube 11 and whichends in its underpressure area in order to achieve pre-atomization. Inthis case, the fuel feed tube 15 discharges in the smaller Venturi tube19 by which air is likewise delivered.

Combustion air is fed into the inlet part 13 of the Venturi tube 11 bymeans of a fan (not shown) and which provides combustion air with only asmall overpressure. The combustion air is delivered along the arrow 17to the Venturi tube 11.

The axial pressure characteristic in the Venturi tube 11 is shown inFIG. 2, in a diagram with the length ε of the Venturi tube 11 plotted onits x axis, and the pressure differential Δp in the Venturi tube 11plotted on its y axis. Accordingly, the combustion air at the inletpoint into the inlet part 13 of the Venturi tube 11 has a lowoverpressure which is achieved by the fan which delivers the combustionair. With flow through the inlet part 13, due to the narrowing of thecross section the speed increases, at the same time the combustion airpressure drops, and in the transition to the subsequent diffuser part12, reaches a minimum value. This minimum absolute pressure correspondsto a maximum underpressure compared to the combustion chamber pressurelevel. This underpressure decreases downstream in the continuation ofthe diffuser part 12 so that the combustion air entering the combustionchamber 10 is roughly at the combustion chamber pressure.

The nozzle 16 has at least one radial hole 18 which discharges into theaxial fuel delivery hole of the nozzle 16. Via this radial hole 18, airis introduced into the delivery path of the liquid fuel so that in thenozzle 16 swirling of the combustion air and liquid fuel occurs. Thismixture then emerges atomized from the outlet opening of the nozzle 16and mixes in the diffuser part 12 with the combustion air which is takenin along the arrow 17 and which is provided to the inlet part 13 by thefan with low pressure.

Moreover, preferably secondary combustion air is supplied to thecombustion chamber 10. For this purpose, at the point at which thediffuser part 12 of the Venturi tube passes into the combustion chamber10, distributed around the periphery, secondary air openings 20 areformed via which secondary air is fed into the combustion chamber 10.There can also be secondary air openings alternatively or additionallyon the jacket of the combustion chamber 10. FIG. 4 schematically shows,in a lengthwise section, the rear part of the combustion chamber of aburner equipped with an embodiment of a Venturi nozzle of the inventionfor an auxiliary motor vehicle heater.

The cylindrical combustion chamber 110 is connected downstream of thecombustion air supply chamber 111 into which combustion air is suppliedby means which are not shown, typically by means of a fan. Thecombustion chamber 110, running coaxially to its lengthwise central axisL which is shown by the dot-dash line, has a connection opening 122 forconnection of the downstream end of the Venturi nozzle 112 which islocated completely within the combustion air supply chamber 111. Aroundthis connection opening 122 is a ring of smaller openings 123 for thepassage of secondary combustion air into the combustion chamber 110.

The Venturi nozzle 112, in the downstream area, comprises a conicaldiffuser 113 which discharges into the combustion chamber 110 and whichtapers in the upstream direction. In the upstream direction, the Venturinozzle 112 comprises a conical inlet part 114 which has a diametervariation which is opposite the diffuser 113, i.e., conically tapers inthe direction toward the diffuser 113. The outside end of the inlet part114 adjoins a cylinder part 115 which discharges into the combustion airsupply chamber 111. The diffuser 113 and the inlet part 114 areconnected via a cylinder part 116 which is small in diameter and intowhich a fuel feed tube 117 discharges. The fuel feed tube 117 runscoaxially to the lengthwise central axis of the Venturi nozzle 112 andis routed out of the combustion air supply chamber 111 at an angleoutside of this nozzle.

In this arrangement of the combustion air supply chamber 111 and theVenturi nozzle 112, liquid fuel is taken into the combustion air by theunderpressure which prevails in the area of the narrowest point (in thearea of the cylinder part 116) and atomized. The combustion air suppliedto the inlet part 114 from the combustion air supply chamber 111,together with the atomized fuel from the Venturi nozzle 112, isdelivered into the combustion chamber 110. The mist of fuel andcombustion air is ignited in the combustion chamber 110 and burned as itis additionally mixed with additional secondary combustion air from theopenings 123. For this purpose, an ignition means 124 projects into thecombustion chamber 110 and its end extends into the area of the exit ofthe conical diffuser 113 of the Venturi nozzle 112.

According to the invention, the Venturi nozzle 112 is axially dividedinto two parts, specifically into a discharge part 118 which borders thecombustion chamber 10, and a supply part 119 which is located upstreamof this discharge part 118. The axial division of the Venturi nozzle 112is made in the area of its diffuser 113 so that the supply part 119 isroughly twice as long as the discharge part 18.

In the preferred embodiment shown in FIG. 4, the discharge part 118 andthe supply part 119 are separated from one another by an annular gap 120with a width which is typically between 0.1 and 0.8 mm. Preferably, thegap width is chosen to be roughly 0.3 mm. In the axial direction, theannular gap 120 is bordered by the facing annular end faces of thedischarge part 118 and the feed part 119 and radially by a ring seal 121which seals the annular gap 120 and thus the conical diffuser 113relative to the outside. The material of the ring seal 121 is preferablya heat-insulating material such as, for example, a ceramic. The Venturinozzle 112 is made of metal, but preferably is also at least partiallymade of a ceramic. The material for the two Venturi nozzle parts 118,119 can be the same. However, preferably, the material of the dischargepart 118 has a lower thermal conductivity than the material of thesupply part 119 in order to transfer as little heat as possible to theannular gap 120 between the two Venturi nozzle parts 118, 119.

Due to the heat-insulated division of the Venturi nozzle 112 of theinvention, it has a cold and a hot part. The upstream cold supply part119 is typically exposed to temperatures below 180° C. in operation dueto the division of the Venturi nozzle into two parts so that cracking ofthe fuel cannot occur in this nozzle part 119. On the other hand, theflame-side hot discharge part 118 of the Venturi nozzle 112 is typicallyexposed to temperatures above 500° C. so that liquid fuel striking itsinside wall from the fuel feed tube 117 vaporizes without leaving crackresidues. Thus, it is ensured that the Venturi nozzle 112 is not cloggedwith residues, and thus, its efficiency is not adversely affected.

The ring seal 121 can fill the entire annular gap 120. Alternatively, itis also conceivable for the ring seal 121 to be completely omitted. Fora very narrow annular gap 120, there is almost no leakage of fuel-airmixture to the outside. Small leaks would be supplied to the combustionchamber with the secondary combustion air and burned there.

As a result of the low pollutant discharge which can be achieved with aburner equipped with the Venturi nozzle in accordance with theinvention, a longer service life of the burner, and thus of the heater,and less environmnental impact are ensured. Finally, the startingbehavior is optimum by the use of the Venturi nozzles according to theinvention.

What is claimed is:
 1. Venturi nozzle for atomization of liquid fuel forcombustion of the fuel in the presence of combustion air in a combustionchamber of a burner, wherein the Venturi nozzle is axially divided intoa fuel/combustion air discharge part and a fuel/combustion air supplypart, and wherein the fuel/combustion air discharge part and thefuel/combustion air supply part are thermally insulated relative to oneanother; wherein facing annular end faces of the discharge and supplyparts of the Venturi nozzle are separated from one another at leastpartially via an annular gap.
 2. Venturi nozzle as claimed in claim 1,wherein the supply part of the Venturi nozzle has a greater axialextension than the discharge part.
 3. Venturi nozzle as claimed in claim2, wherein the supply part of the Venturi nozzle is roughly twice aslong as the discharge part.
 4. Venturi nozzle as claimed in claim 1,wherein the discharge part of the Venturi nozzle is made of a materialwith a thermal conductivity which is poorer than that of the supplypart.
 5. Venturi nozzle as claimed in claim 1, wherein the annular gapis radially bordered by a ring seal.
 6. Venturi nozzle as claimed inclaim 1, wherein the annular gap has a gap width between 0.1 and 0.8 mm.7. Venturi nozzle as claimed in claim 1, wherein the annular gap has agap width of roughly 0.3 mm.
 8. Venturi nozzle as claimed in claim 1,wherein the fuel/combustion air discharge and a part and afuel/combustion air supply part are separated from each other at adiffuser part of the Venturi nozzle.
 9. Venturi nozzle as claimed inclaim 1, wherein at least the discharge part is made of a ceramicmaterial.
 10. Venturi nozzle for atomization of liquid fuel forcombustion of the fuel in the presence of combustion air in a combustionchamber of a burner, wherein the Venturi nozzle is axially divided intoa fuel/combustion air discharge part and a fuel/combustion air supplypart, and wherein the fuel/combustion air discharge part and thefuel/combustion air supply part are thermally insulated relative to oneanother; wherein the discharge part and the supply part are separatedfrom one another by a ring seal which axially borders facing annular endfaces of the discharge and supply parts essentially over the entiresurface thereof.
 11. Venturi nozzle as claimed in claim 10, wherein thering seal is made of a thermally insulating material.
 12. Venturi nozzleas claimed in claim 10, wherein the ring seal is made of a ceramicmaterial.
 13. Burner for an auxiliary motor vehicle heater, comprising:a combustion chamber for combustion of liquid fuel in the presence ofcombustion air; and a mixing means which comprises a nozzle foratomization of liquid fuel, the nozzle comprising a Venturi tube or aVenturi nozzle with an inlet part which tapers in flow direction of thecombustion air and with a diffuser part which widens in the flowdirection of the combustion air, the diffuser part having a largerdiameter end which discharges into the combustion chamber in anunderpressure area in a transition area from the inlet part to thediffuser part; wherein at least the diffuser part of the Venturi tube orVenturi nozzle is made of a ceramic material, wherein a fuel feed tubeis provided for supplying fuel to the Venturi tube or Venturi nozzle,the fuel feed tube being located coaxially relative to a lengthwisecenter axis of the Venturi tube or Venturi nozzle and having an outletopening located at the narrowest point between the supply Dart and thediffuser part.
 14. Burner as claimed in claim 13, wherein at least thefront section of the diffuser part is formed integrally with thecombustion chamber.
 15. Burner as claimed in claim 13, wherein thediffuser part diverges in a conical shape in toward the combustionchamber and has sections of differing opening angles.
 16. Burner asclaimed in claim 13, wherein the combustion chamber has at least oneinlet for secondary combustion air.
 17. Burner as claimed in claim 16,wherein the at least one inlet for secondary combustion air, viewedaxially, is in an area of the combustion chamber in which the Venturitube or Venturi nozzle discharges.
 18. Burner as claimed in claim 13,wherein the Venturi tube or Venturi nozzle is a binary nozzle having oneof a pre-atomization nozzle and a second smaller Venturi tube, an inletand outlet opening of which is located in the Venturi tube or Venturinozzle at a location at which a pressure drop produced by the Venturitube or Venturi nozzle will create a flow therethrough.
 19. Burner asclaimed in claim 13, further comprising combustion air supply fordelivering air to said inlet part.